[v3 PATCH] Reduce the size of variant, it doesn't need an index of type size_t internally.

[Jonathan Wakely]

On 11/01/17 10:29 +0000, Jonathan Wakely wrote:
>On 11/01/17 00:19 +0200, Ville Voutilainen wrote:
>>@@ -1086,7 +1099,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>      { return !this->_M_valid(); }
>>
>>      constexpr size_t index() const noexcept
>>-      { return this->_M_index; }
>>+      {
>>+	if (this->_M_index ==
>>+	    typename _Base::_Storage::__index_type(variant_npos))
>>+	  return variant_npos;
>>+	return this->_M_index;
>
>GCC doesn't seem to be smart enough to optimize the branch away here.

But that's only for 32-bit x86. It optimizes well for x86_64, so no
need to obfuscate it.